This invention relates to a power transmission device which is mounted between a driven machine such as a power lawn mower which serves, and a prime mover as the driver.
As a power transmission device for transmitting torque produced by a rotary machine as a driver to the rotary part of a driven machine to cause rotation of the latter, a clutch brake assembly has been proposed by U.S. Pat. No. 4,377,224 issued Mar. 22, 1983, which comprises: an annular operating element externally operative for rotational movement through a predetermined circumferential angle; a cylindrical input hub arranged concentrically of the operating element and rigidly fitted on an output shaft of a rotary machine as a driver; an output hub having an axially extending boss portion and arranged concentrically of the output shaft for rotation relative thereto; an annular friction plate spline-fitted on the boss portion of the output hub for rotational movement together with the output hub for axial displacement relative to the output hub for frictional engagement with the input hub; urging means resiliently urging the friction plate toward the input hub; an annular brake element interposed between the operating element and the friction plate for axial displacement into frictional engagement with the friction plate; guide means for the brake element, for permitting axial displacement of the brake element and prohibiting circumferential displacement of same; and a plurality of balls rollingly held between the operating element and the brake element. Axial displacement of the brake element in a direction toward the operating element causes frictional engagement of the input hub with the friction plate to thereby permit transmission of torque from the input hub to the output hub, and axial displacement of the brake element in a direction away from the operating element causes disengagement of the friction plate from the input hub to thereby interrupt frictional engagement of the brake element with the friction plate to thereby cause braking of the output hub.
In a conventional power lawn mower composed of a mower cutter, a prime mover and a power transmission device, the component parts of the power transmission device as constructed above are successively mounted onto an output shaft of the prime mover which may be an engine, to assemble the power transmission device and mount same onto the prime mover at the same time. Therefore, if the maker of the prime mover is not the same as the maker of the power transmission device, those who are not skilled in the manufacture of such power transmission devices will have to mount the power transmission device while simultaneously assembling same, for themselves.
This means that persons concerned with either the maker of the lawn mower who is usually supplied with prime movers completed as finished products and finally adjusted from the prime mover maker, or the prime mover maker who is also the maker of the lawn mower, will be compelled to perform the operation of mounting the component parts of the power transmission device onto the prime mover while simultaneously assembling same. This can result in poor fine adjustment of the assembled power transmission device, often leading to occurrence of a fault in the same device.
Therefore, it has been strongly desired by the lawn mower maker that the power transmission device maker should supply their product or power transmission device in an already assembled and adjusted state to the lawn mower maker, so that the latter has only to merely mount the power transmission device onto the prime mover.
Furthermore, a lawn mower should desirably be as compact in size and light in weight as possible. To this end, a power transmission device for use in such a lawn mower should have the smallest possible axial size and the smallest possible number of component parts.